1. Field of the Invention
The invention relates generally to plastic blow molded containers such as refuse containers and, more specifically, to methods of reinforcing such articles to achieve enhanced strength characteristics and reduced cost of manufacture.
2. The Prior Art
The blow molding process is commonly used in the production of containers for various applications. For example, many commercially available refuse containers, comprising a lid and a base, are manufactured by such a process. Conventional blow molding apparatus manufacture containers by means of blow molding from tubular preforms or parisons which are extruded of plastic by extruder heads from plastics material which has been plasticized in extruders. The discharge nozzle from which the platicized material exits to create the preform typically includes a die ring having a center aperture and a frustro-conical die pin that is received into the die ring aperture. The spacing between the outer surfaces of the die pin and the outward directed surfaces of the die ring which define the aperture is adjustably controlled by movement of the die pin in and out of the die ring.
From the extruder, plastic is pressured downward between the die pin and the die ring, forming a hollow parison which is suspended between two mold halves. The parison is then expanded outwardly by the injection of air into the center and reforms against the mold sidewalls. The air can be injected from the top through the die pin or, alternatively, from the bottom of the mold cavity. After the plastic sets against the mold sidewalls, the mold is open and the hollow article formed thereby is extracted.
U.S. Pat. Nos. 4,889,477 and 4,297,092, incorporated herein by reference, illustrate the general state of the art apparatus for blow molding hollow objects. The process works well and may be used to form hollow bodies for a variety of applications. For example, Design U.S. Pat. No. 326,342 shows a refuse container that is preferrably formed by a gas-assisted molding technique. The container comprises a lid and a base, both integrally formed from the same parison. Subsequent to the molding operation, the lid and the base are severed into independent components. An advantage to forming articles by this method is that the walls of the container and lid can be thinned to a great degree, thereby conserving plastic and reducing costs. However, in making the walls of thinner stock, the container and base can lose its structural rigidity and integrity. The resultant product, while functional for its intended purpose, can be perceived as being structurally inferior to containers formed by other means.
To compensate for reduced rigidity resulting from thinning the wall stock, designers of containers have incorporated shoulders and recesses into the external wall surface. These structural elements are effective in increasing the hoop strength and rigidity of the containers. However, forming shoulders and recesses into the sidewalls can detract from the aesthetic appeal of the exterior of the container and limits design alternatives.